Running apache with admin privilegie is a big security risk(Drop it ASAP)
net user Myapacheuser somestrongpasswd /ADD
launch it from that User

MySQL 5 is running on administrator account.

Security risk.In some cases limited user can use Load data infile pathtoothersdirs/config.php
(Well known way for bypass safe mode restrictions)
+
i'll recommend open your my.ini (MYSQL config file)
secure_file_priv="c:/somejunkpath"
save and restart the MYSQL service.
This will prevent you from
select ... into out file
+ from
Load data infile pathtoothersdirs/config.php

PHP 5 module is loaded on the apache server with administrator user. (can write on directoryes/files) (users home directory)

Is here any open_basedir restriction?(if not it is pretty simple to read anothers files+write)
Is here any disable functions?(PHP disabled functions?)(if not you are vulnerable)
Is here cgi enabled? If yes machine is fully vulnerable.

Users can upload files to their home directory (ftp)(the ftp i secure)
If user A have files on /home/userA ,
is it possible for user B to upload a php script to his home direcotry /home/UserB,

Possible.If it is vulnerable software(outdated and has 0day) this is possible.
Also this is possible if FTP isn't correctly administered.
From which privilegie it runs? If it administrator or LOCAL SYSTEM it is a big whole!(drop it to user privilegie too)

can this scrip change/write/delete files on user A's home directory /home/userA ??
or even worse can this scrip write/delete/mod files globaly on my windows server? (like c:\windows..., or read c:\secure\.htpassword files)

This is a really complex things.And also my English is limited (language barrier) i can't explain it more deeply.But i can say that it is not correctly administering.

Also always keep in mind 1'stly always keep up2date your OS.

On another hand nothing unhackable.Everything it has own vulnerabilities even our psychology too(In eg: Social Enginneering attacks against humans)
Here is few resources for you:
packetstormsecurity.com
exploit-db.com

You can find a lot of whitepapers there which is vital especially for server administrators.